MAGNETORHEOLOGICAL FLUIDS

DHANYA P. NAIRMECHANICAL DEPARTMENT(1MJ07ME017)

INTRODUCTION

A smart fluid is a fluid whose properties (for example the viscosity) can be changed by applying an electric field or a magnetic field.

A magnetorheological fluid (MR fluid) is a type of smart fluid in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid.

DEFINITION

A low-viscosity fluid containing a

suspension of micrometer-size magnetic particles that increases in viscosity proportionally to the strength of an applied magnetic field.

COMPOSITION

Typical MR fluid consists of these three parts:Carbonyl Iron Particles -- 20 to 40

percent of the fluid is made of these soft iron particles that are just 3 to 5 micrometers in diameter.

A Carrier Liquid -- The iron particles are suspended in a liquid, usually hydrocarbon oil. 

Proprietary Additives -these additives are put in to inhibit gravitational settling of the iron particles.

HOW IT WORKS

The magnetic particles are suspended within the carrier oil, distributed randomly and in suspension under normal circumstances

When a magnetic field is applied, however, the microscopic particles (usually in the 0.1–10 µm range) align themselves along the lines of magnetic flux.

MODES OF OPERATION

An MR fluid is used in one of three main modes of operation, these being flow mode, shear mode and squeeze-flow mode. 

FLOW MODE

Fluid flowing as a result of pressure gradient between two stationary plates

SHEAR MODE

Fluid between two plates moving relative to one another.

SQUEEZE-FLOW MODE

Fluid between two plates moving in the direction perpendicular to their planes.

APPLICATIONS

Seat suspensions Vehicle suspensions Clutches Brake system Robotics Design of buildings and bridges Home appliances like washing machine etc.

MR fluids find a variety of applications They are widely used in:

VEHICLE SUSPENSION DAMPERS The MR damper has

a built-in MR valve across which the MR fluid is forced.

The piston of the MR damper acts as an electromagnet with the required number of coils to produce the appropriate magnetic field.

Also the MR damper has a run-through shaft to avoid an accumulator.

MR TRANSMISSION CLUTCHES They are used in

automotive power train to transmit torque from the engine to the transmission and the vehicle.

The MR sponge clutch may be used to provide launch control of an automobile thereby achieving smooth vehicle launch.

The MRF clutch thus may replace the existing torque converters and therefore help increase the fuel economy.

MR BRAKE

Basic design of MR Brake

PROTOTYPE OF AN MR BRAKE

MR DAMPING IN WASHING MACHINE

A variable damping system based on magnetorheological fluid sponges can help control the vibratory motion of a household washing machine during its spin cycle.

Damping is switched on as the drum passes through resonance and off again at the highest speeds for optimum vibration isolation.

The system permits the drum to rotate at speeds high enough to function as a centrifuge, but without the violent shaking familiar to every user.

MR TECHNOLOGY USED IN PROSTHETIC JOINT

Collaborating with design engineers, Biedermann Motech, a German manufacturer of prosthetic components, developed a device that improves the mobility of above-the-knee leg amputees.

The Prolite™ Smart Magnetix™ Above-the-Knee (AK) Prosthetic, increases gait balance, stability and energy efficiency using controllable MR technology adapted from LORD Motion Master™ Ride Management System truck seat damper

MR FLUID IN SEISMIC AND WIND MITIGATION

Civil engineers in the construction industry are incorporating MR Technology into the structural engineering of buildings and bridges.

A damping system utilizing MR fluid dampers works similarly to an automotive shock absorber, protecting the structure from earthquakes and windstorms.

MR Dampers are currently being used on the Dongting Bridge in China.

ADVANCEMENTS IN MR FLUID TECHNOLOGY

Now under commercial development are very large MF fluid dampers designed for seismic damage mitigation in civil engineering structures such as buildings and bridges.

The technology is being investigated for applications in vehicular steer-by-wire devices.

The nervous systems of future robots might use MR fluids to move joints and limbs in lifelike fashion.

Book makers could publish rippling magnetic texts in Braille that blind readers could actually scroll and edit.

BUT...

High density, due to presence of iron, makes them heavy.

High-quality fluids are expensive.

Fluids are subject to thickening after prolonged use and need replacing.

Settling of Ferro-particles can be a problem for some applications.

CONCLUSION

Magneto rheological fluids are actually amazing magnetic fluids.

MR fluid development is of course a balancing act that is highly coupled with MR device design.

MR fluid durability and life have been found to be more significant barriers to commercial success than yield strength or stability.

Thus MR fluids can be considered as a better way of controlling vibrations.

The key to success in all of these implementations is the ability of MR fluid to rapidly change its rheological properties upon exposure to an applied magnetic field.